A long-term goal of this research is to determine the molecular basis for the regulation of electron transfer reactions in enzymes by binding of protein components and substrate/product and effector molecules. The electron transfer reaction in ribonucleotide reductase is regulated by complex formation between R1 and R2 and the binding of substrate/product and the activity of allosteric effectors, dATP and ATP. Regulation may occur by subtle conformational or hydrogen bond shifts which may be observed by potential shifts in a redox active center in the enzyme. Therefore, the effects of the binding of nucleotides to the R1/R2 will be determined by redox potential studies of the dinuclear iron cluster in RS using spectroelectrochemistry. The electron path between R1 and R2 is proposed to follow a specific path of amino acids and hydrogen bonds and includes one of the iron atoms in diiron cluster. This pathway will be tested by studying the kinetics of the reduction of wild type R2/OX and several mutants by electrochemically reduced methyl viologen.